Isolation of the lactose permease protein is a necessary prerequisite to the study of its structure and function. This transport protein will be detergent extracted from the E. coli inner membrane and purified by molecular sieve and hydrophobic chromatography. The permease is the product of the y gene, one of three structural genes in the lactose operon. The protein products of these genes, and the lac repressor protein specified by the adjacent i gene, all contain binding sites for beta-galactosides. Determination ofthe primary structure of the y gene product will allow a search for sequence homologies within the lac operon to test the role of gene duplication in operon evolution. The lactose permease is also representative of a large class of transport proteins that utilize the membrane potential to drive active transport. Studies of the structure of the isolated protein, and its orientation in the membrane, will reveal the relationship of protein tertiary structure to transport mechanism and coupling to energy metabolism. Permease isolated from y gene mutant strains will be used to correlate functional deficiencies with specific structural alterations. Antibodies produced to the isolated membrane protein will be used to identify the primary translation product of the lac y message. Comparison of the nascent protein to the mature membrane protein will indicate whether a precursor form is synthesized and cleaved during membrane insertion. This will provide a test of the applicability of the "signal" hypothesis to synthesis of an integral membrane protein.